Lower Chlorophyll Content Research Articles

Biogeochemical patterns in the Atlantic Inflow through the Strait of Gibraltar

The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena are defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides).During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3–0.4mgm−3) are found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics.In contrast, during spring tides, patches of water with high chlorophyll levels (0.7–1mgm−3) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and can account for around 30% of total annual nitrate transport into the Mediterranean basin. Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport).

Relationship between Artemia population dynamics and chlorophyll a fluctuations in Urmia Lake (Iran)

Determination of chlorophyll a is one of the most common methods for measuring the primary production in the lakes and sea water. We studied Artemia Leach. dynamics and chlorophyll a fluctuation and their relationship in Urmia Lake. Sampling was performed monthly during one year (2007) at eleven sampling stations in Urmia Lake. Population dynamics analysis of Artemia from Urmia Lake suggested that the highest diversity in various Artemia morphological stages was present from May to July and the highest densities in March. On the other hand, no morphological stages were observed, at all stations in the lake, from January to April. The mean chlorophyll a concentration in Urmia Lake was 0.8 µg.L-1, and the highest and the lowest concentrations of chlorophyll a were measured in June and July with 2.53 µg.L-1 and 0.1 µg.L-1 respectively. According to the Carlson classification Urmia Lake was oligothrophic. Artemia biomass appeared in the mid spring and bloomed in the summer. Generally, there was a negative relationship between Artemia population and chlorophyll a.

Relationship between wind speed and sea salt aerosol production: A new approach

A relationship between ocean surface wind speed and sea salt aerosol production is established through a study carried out using the aerosol flux continuity equation by introducing satellite data on aerosols and ocean surface wind speed into it. This mathematical approach eliminates interferences from background aerosols and aerosol variations due to advection and convergences/divergences in wind field and correctly estimates the rate of sea salt aerosol production by winds. To avoid oceanic biogenic sources and transport from other oceanic and land regions, the study is done over ocean sites substantially remote from the continents with low chlorophyll concentrations (<0.06mg/m3) and restricting to aerosols in the bottom layer (<0.5km altitude) of the atmosphere. The surface wind speed is found to correlate better with the estimated aerosol production rate (RWS=0.99, p<0.0001) than with the bottom layer aerosol optical depth (RWB=0.97, p<0.0001). Aerosol production is observed at wind speeds even below 4m/s and the production rate is found to follow a linear relationship with ocean surface wind speed with a slope 0.0053 and an intercept 0.0163 for low as well as high winds.

Photosynthesis, ion accumulation, antioxidants activities and yield responses of different cotton genotypes to mixed salt stress

This study analyzes the effects of soil salinity on photosynthetic character, osmoregulation, content of pigment, K+/Na+ ratio, lipoxygenase and antioxidants activities in functional leaves during the flowering and boll-forming stages of two cotton cultivars, namely, CCRI-44 (salt-tolerant) and Sumian12 (salt-sensitive), grown under different soil salinity conditions. In the control plants, non-significant differences were found in gas exchange, saturation irradiance (SI) and carotenoid (Car) content between the two cultivars. However, it showed higher K+/Na+ ratio, antioxidant enzyme activities, soluble sugar and protein contents, and lower chlorophyll (Chl) content and yield in CCRI-44. Salinity stresses remarkably increased soluble sugar and protein contents, lipoxygenase and the antioxidant activities, but decreased K+/Na+ ratio, Chl and Car contents, SI, photosynthetic capacities and yield, the extent being considerably larger in Sumian12 than CCRI-44. Although the soluble sugar, protein contents and the antioxidant activities of Sumian12 elevated more evidently under salt stresses, those variables never reached the levels of CCRI-44. Thus, CCRI-44 could maintain higher seed cotton yield than Sumian12 by sustaining higher osmoregulation and antioxidative abilities, which led to higher photosynthetic capacity. Hence, the salt-tolerant cotton cultivars could harmonize the relationship between CO2 assimilation (source) and the seed cotton yield (sink) under the experimental conditions. Key words: Cotton (Gossypium hirsutum L.), mixed salt stress, salt tolerance, photosynthesis, ion accumulation, antioxidant enzyme activity, seed cotton yield.

Influence of mesoscale eddies on biological production in the Mozambique Channel: Several contrasted examples from a coupled ocean-biogeochemistry model

The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the model, several cyclonic eddies were found with low concentrations of chlorophyll at their cores, which contrasts with previous studies in the open ocean. In addition, several anticyclonic eddies were simulated with high concentrations of chlorophyll at their cores. Phytoplankton growth within these mesoscale features (both cyclonic and anticyclonic eddies) occurred in response to nutrient injection into the euphotic zone by advection, and subsequent retention of surrounding nutrient-rich waters within eddies. Offshore nutrient distributions depended strongly on lateral advection of nutrient-rich water from the coastal regions, induced by eddy interaction with the shelf. The environmental conditions at the locations where eddies were generated had an important effect on nutrient concentrations within these structures.

Shoot Feeding as a Nutrient Acquisition Strategy in Free-Living Psylloids

Shoot feeding by sucking insects is accepted as an adaptation to feeding where plant nutrients are most concentrated and/or of higher quality. Psylloids are an important hemipteran taxon, most of which are free-living and comprise many shoot feeding species, whose nutritional ecology has been largely ignored. I conducted a longitudinal study of Ctenarytaina eucalypti (Maskell) and C. bipartita Burckhardt et al. (Aphalaridae) feeding on eucalypts to document how within-plant (ontogenic) variation in nutritional quality, in particular of free amino acids, determines host suitability and hence the distribution and abundance of nymphs. Nymphs were most abundant within developing apical buds but were not more abundant on branchlets of greater vigour (indicated by rate of extension). Nymphs could be found up to two (C. bipartita) to three (C. eucalypti) alternate leaf pairs distant from apical buds but infrequently and in low numbers; they were never found on older, fully expanded leaves. The position of a leaf on a branchlet (indicative of age) determined its nutritional quality. Younger leaves had higher water contents, lower chlorophyll contents and differed in amino acid (essential and non-essential) composition compared to older leaves. The abundance of C. eucalypti nymphs on expanding leaves and in buds was positively correlated with the concentrations of methionine, valine and threonine in E. globulus leaves at the same or comparable position on a branchlet. The abundance of C. bipartita nymphs was positively correlated with foliar leucine concentrations. Shoot feeding by these two psyllids facilitates access to more concentrated, better quality plant nutrients but may not entirely explain the adaptive significance of their behaviour. The humid microclimate created by the architecture of the hosts’ apical buds protects eggs and nymphs from desiccation and is suggested to have had a significant influence on the evolution of host utilisation strategies of psyllids within this genus.

Seasonal Cycle of Phytoplankton Community Composition in the Coastal Upwelling System Off Central Oregon in 2009

Coastal upwelling in the northern California Current varies seasonally, with downwelling in winter and upwelling in summer, resulting in pronounced variability in hydrography, nutrients, phytoplankton biomass, and species composition. Winter was characterized by moderate concentrations of nitrate and silicate (averages of 10 and 18 μM, respectively) and low concentrations of chlorophyll a (Chl a). During the upwelling season, concentrations of the same nutrients ranged from near 0 μM to approximately 27 and 43 μM and Chl a 0.5 < x < 15 μg L−1. During autumn, upwelling weakened and nutrient concentrations were reduced, but large phytoplankton blooms continued to occur. Variations in hydrography, nutrients, and phytoplankton also occurred within the upwelling season due to alternation of the winds between northerly (active upwelling) and southerly (relaxation of upwelling), on a 5- to 10-day time scale. Eleven blooms were observed, most of which occurred near the end of active upwelling events and during relaxation of upwelling. Nonmetric multidimensional scaling ordination of species composition of the microplankton revealed four distinct communities: a winter community, early upwelling and late upwelling season communities, and an autumn community. Diatoms (Asterionellopsis glacialis, Eucampia zodiacus, and several Chaetoceros, Thalassiosira, and Pseudo-nitzschia species) dominated early in the upwelling season, averaging 80 % of the phytoplankton biomass, and dinoflagellates dominated near the end of the upwelling season, averaging 68 % of the phytoplankton biomass. Dinoflagellates formed two monospecific blooms—Prorocentrum gracile in late summer and Akashiwo sanguinea in autumn. Changes in community composition were correlated with bottom temperature and salinity (representing seasonal variability) and sea surface salinity (representing within-season event-scale variability in upwelling).

Biochemical and anatomical responses related to the in vitro survival of the tropical bromeliad Nidularium minutum to low temperatures

Nidularium minutum is a tropical bromeliad that grows in natural environment with temperatures ranging from 2 to 30 °C. In the present work we cultivated this species in vitro at 5, 10, 15, and 25 °C for 3 and 6 months aiming at assessing biochemical and morphological responses that allow its survival under low temperatures. No survival was observed for plants cultured constantly at 5 °C and the lowest biometric parameters were found for those grown at 10 °C. A thick aquiferous parenchyma, accumulation of reducing sugars, and increased pectin content in the cell walls were observed in plants grown at 10 and 15 °C when compared to those maintained at 25 °C. In plants cultured at 10 °C, leaf bleaching correlated with low chlorophyll content and lower survival rate after 6 months when compared to those grown at 15 °C. The best in vitro culture condition for slow growth and plant acclimatization was found to be at 15 °C. This probably correlated with the immediate availability of carbon to restore growth during acclimatization and also with higher root initiation under this condition. This study brings information about the responses related to functional adaptation to low temperatures in N. minutum cultured in vitro that can also be implicated in its survival under natural conditions. Additionally, it suggests the best temperature to form a minimal growth collection to be used in restocking and conservation programs for endangered tropical bromeliads.

Dimethyl disulfide produced by the naturally associated bacterium bacillus sp B55 promotes Nicotiana attenuata growth by enhancing sulfur nutrition.

Bacillus sp B55, a bacterium naturally associated with Nicotiana attenuata roots, promotes growth and survival of wild-type and, particularly, ethylene (ET)-insensitive (35)S-ethylene response1 (etr1) N. attenuata plants, which heterologously express the mutant Arabidopsis thaliana receptor ETR1-1. We found that the volatile organic compound (VOC) blend emitted by B55 promotes seedling growth, which is dominated by the S-containing compound dimethyl disulfide (DMDS). DMDS was depleted from the headspace during cocultivation with seedlings in bipartite Petri dishes, and (35)S was assimilated from the bacterial VOC bouquet and incorporated into plant proteins. In wild-type and (35)S-etr1 seedlings grown under different sulfate (SO(4)(-2)) supply conditions, exposure to synthetic DMDS led to genotype-dependent plant growth promotion effects. For the wild type, only S-starved seedlings benefited from DMDS exposure. By contrast, growth of (35)S-etr1 seedlings, which we demonstrate to have an unregulated S metabolism, increased at all SO(4)(-2) supply rates. Exposure to B55 VOCs and DMDS rescued many of the growth phenotypes exhibited by ET-insensitive plants, including the lack of root hairs, poor lateral root growth, and low chlorophyll content. DMDS supplementation significantly reduced the expression of S assimilation genes, as well as Met biosynthesis and recycling. We conclude that DMDS by B55 production is a plant growth promotion mechanism that likely enhances the availability of reduced S, which is particularly beneficial for wild-type plants growing in S-deficient soils and for (35)S-etr1 plants due to their impaired S uptake/assimilation/metabolism.

Reduction of methylviologen-mediated oxidative stress tolerance in antisense transgenic tobacco seedlings through restricted expression of StAPX

Ascorbate peroxidases are directly involved in reactive oxygen species (ROS) scavenging by reducing hydrogen peroxide to water. The tomato thylakoid-bound ascorbate peroxidase gene (StAPX) was introduced into tobacco. RNA gel blot analysis confirmed that StAPX in tomato leaves was induced by methylviologen-mediated oxidative stress. The sense transgenic seedlings exhibited higher tAPX activity than that of the wild type (WT) plants under oxidative stress conditions, while the antisense seedlings exhibited lower tAPX activity. Lower APX activities of antisense transgenic seedlings caused higher malondialdehyde contents and relative electrical conductivity. The sense transgenic seedlings with higher tAPX activity maintained higher chlorophyll content and showed the importance of tAPX in maintaining the optimal chloroplast development under methylviologen stress conditions, whereas the antisense lines maintained lower chlorophyll content than WT seedlings. Results indicated that the over-expression of StAPX enhanced tolerance to methylviologen-mediated oxidative stress in sense transgenic tobacco early seedlings, whereas the suppression of StAPX in antisense transgenic seedlings showed high sensitivity to oxidative stress.

The turbidity front as a habitat for Acartia tonsa (Copepoda) in the Río de la Plata, Argentina-Uruguay

Acartia tonsa is one of the most abundant copepod species in estuaries worldwide. In the Río de la Plata, its highest densities appear to occur in an area of low quality food (detritus): the turbidity front (TF). The objective of this study was to understand how trophic and oceanographic drivers contribute to the high densities of A. tonsa in the Río de la Plata TF. The patterns of spatial distribution and density of this species were analyzed in relation to oceanographic and biological attributes of the system. The egg production rate (EPR) in the TF was evaluated as a measure of fitness, and a stable isotope analysis indicated the possible sources of organic matter in the species' diet. This study confirmed that the highest observed densities of A. tonsa were mostly associated with the TF, where high suspended matter and low Chl-a occur. Immediately offshore from the TF, decreased copepod densities and the maximum Chl-a values were found. Females close to the estuarine turbidity maximum (ETM) had a lower EPR than those closer to the high Chl-a concentrations. Within the TF, A. tonsa apparently fed on detritus close to the ETM and phytoplankton close to the edge of the TF. The report includes a discussion of how retention processes, two layered flow and the life history strategy of A. tonsa could be contributing to the development of high densities (more than 10,000indm−3) of this species in the inner estuarine zone, despite the poor quality of food available for development in that area. A. tonsa can live and prosper in areas with high turbidity and low chlorophyll concentrations. This trait exemplifies the plasticity of this species and helps explain why it is a key species in many worldwide estuaries.

The summer foraging ranges of adult spectacled petrels Procellaria conspicillata

AbstractSatellite transmitters were attached to eight adult spectacled petrels Procellaria conspicillata Gould captured during the early incubation period at their breeding grounds on Inaccessible Island, one of the Tristan da Cunha Islands in the central South Atlantic Ocean. Data on their at-sea distribution was obtained for up to six months. All birds remained within the South Atlantic from 24–44°S, with most between 25 and 40°S. Breeding birds mainly foraged in oceanic waters, but failed breeders or non-breeders concentrated their foraging activity over the Rio Grande Rise and the Walvis Ridge and along the shelf break off the east coast of South America. Little foraging occurred along the Benguela shelf break off southern Africa. Non-breeders favoured relatively warm water with low chlorophyll concentrations, reducing the risk of bycatch in fisheries. Tracked birds spent 16% of their time in areas with high levels of tuna longline fishing activity, with overlap greater for non-breeding birds (22%) than breeding birds (3%). Birds in this study foraged in shallower waters along the continental shelf edge off South America than spectacled petrels tracked in this area in winter, potentially increasing their risk of exposure to demersal longline fisheries in this area in summer.

Functional analyses of nanoparticle toxicity: A comparative study of the effects of TiO2 and Ag on tomatoes (Lycopersicon esculentum)

Engineered nanoparticles (NPs), increasingly used in industry, enter and migrate through biological ecosystems. NPs may create some acute toxicity, but their overall effects on living organisms remain largely unknown. In particular, the behavior of NPs in natural conditions and their consequent ecological effects are still poorly understood. In this study, we developed methods to test the phytotoxicity of two distinctly different NPs, one aerosol (nano-TiO2), and the other colloidal silver (AgNP), by specifically considering their tendencies to agglomerate and form precipitates. First we examined effects of these NPs on germination and root elongation. While exposure to neither of these NPs resulted in acute toxicity on germination, silver NPs caused significantly decreased root elongation at every concentration we tested. We found that the hydrodynamic diameters of AgNPs were much smaller than those of nano-TiO2, which induced higher uptake and phytotoxicity. Based on the agglomeration behavior of the NPs, greenhouse trials were run using commercial soil, for nano-TiO2, and Hoagland's solution, for AgNP. Phytotoxicity of silver NPs in the mature plants was demonstrated by lower chlorophyll contents, higher superoxide dismutase activity and less fruit productivity, while nano-TiO2 resulted in higher superoxide dismutase activity at the highest concentration (5000mg/kg). Both nano-TiO2 and AgNPs were taken up into plant stems, leaves and fruits. Our results suggest that further studies of the ecological effects of nanoparticles and steps to mitigate appropriate management strategies are required.

Commercially-cultured oysters (Crassostrea gigas) exert top-down control on intertidal pelagic resources in Willapa Bay, Washington, USA

The capacity of filter feeders to reduce seston and phytoplankton concentrations in the water column has important implications for restoration and management of coastal ecosystems. We directly measured changes in chlorophyll a concentration on commercially stocked intertidal oyster beds (Crassostrea gigas) in Willapa Bay, Washington, USA by recording water properties near small drifters as they tracked parcels of water across tide flats. Chlorophyll declined 9.6% per half hour in water passing on-bottom adult oysters and 41% for longline adult oysters, whereas chlorophyll concentrations increased as water flowed across tide flats without adult oysters. Field filtration rates, which were fit to exponential declines in chlorophyll and accounted for oyster density and water depth, averaged 0.35Lg−1h−1 (shucked dry weight) for on-bottom aquaculture and 0.73Lg−1h−1 for longline culture, compared to values of 2.5–12Lg−1h−1 reported from laboratory studies of C. gigas. Field filtration rates may be lower than laboratory rates due to unfavorable field conditions (e.g., low initial chlorophyll concentrations) or masked by resuspension of benthic microalgae. In addition to distinctions among on-bottom, longline, and no-oyster habitats, Akaike's Information Criterion analysis showed temperature, initial chlorophyll concentration, and depth related to chlorophyll decline. This research corroborates mathematical models suggesting that benthic suspension feeders are exerting top-down control of pelagic production in this estuary, with strong patterns in chlorophyll emerging across extensive tideflats populated by C. gigas despite low field filtration rates.

Influence of Water Column Chlorophyll Concentration on Bathymetric Estimations in the Lagoon of New Caledonia, Using Several MERIS Images

An estimation of bathymetry in the optically complex lagoon of New Caledonia was performed from multispectral satellite images. Bathymetric estimation was obtained with Medium Resolution Imaging Spectrometer (MERIS) images acquired at different dates. The method is based on the rotation of a pair of spectral bands (red and green bands). One of the resulting images is only depth-dependent when the other is reflectance-dependent. A comparison was made with a compilation of bathymetric data from Institut de Recherche pour le Développement (IRD) Nouméa measurements. This study shows the influence of the variation of water composition, and then of the diffuse attenuation, on bathymetric results. The variation of chlorophyll concentration, correlated with variation of diffuse attenuation, explains the error of the estimation map. The results show that this method remains valid under a low (<;1 mg · m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) and constant concentration (<;10% of variation) of chlorophyll to limit the variation of RMSE in the image on the bathymetric estimation (<; 15.5%).

Determination of physiological parameters of Tilia cordata Mill. in different environments cultivation

This experiment investigated the effect of different container design on growth and development of Small-leaved lime (Tilia cordataMill.). Experimental plants acquired in the Netherlands were of standardized height 0.4 meters, with diameter of the root neck of 3–5 mm. To monitor the effect of different types of containers (“Air-Pot™” container – Bohemiaseed, s. r. o., Squared containers “Vet” – SINCO Ltd., Containers 50 Series MCI/MCC – round plastic nursery containers, “Air pot” garden bags – Arbo ® Standard, Poland) on the physiological and morphological parameters of plants, three types of nursery containers were selected with open ground as control variant. Statistically significant difference between fluorescence and time of measurement was also found. In the Small-leaved lime the container type did not affect chlorophyll content or chlorophyll fluorescence (Fv/Fm); plants grown in Containers 50 Series MCI/MCC showed a lower chlorophyll content compared to plants grown in “Air-Pot ™” containers. As reported in literature, Fv/Fm ratio is a reliable indicator of the occurrence of environmental stresses, including water stress, on air-pot bag for several woody and herbaceous species.

Validation of OCM-2 sensor performance in retrieving chlorophyll and TSM along the southwest Bay of Bengal coast

The Chlorophyll and Total Suspended Matter (TSM) data retrieved from Ocean Colour Monitor (OCM-2) onboard Oceansat-2 were tested for the accuracy using in-situ measurements made along the southwest Bay of Bengal coast during cruises and monthly samplings synchronized with satellite overpass from January 2010 to May 2011. The observed range of in-situ chlorophyll a and TSM concentrations were 0.10–4.60 μgl − 1 and 12.70–34.56 mgl − 1 respectively, while OCM-2 derived chlorophyll a and TSM concentration ranged from 0.324 to 1.552 μgl − 1 and 3.537 to 32.11 mgl − 1, respectively. The in-situ dataset was grouped into low (0.1–0.5 μgl − 1), moderate (0.51–1.0 μgl − 1) and high (>1 μgl − 1) chlorophyll concentration and low (12.7–17.81 mgl − 1), moderate (18.1–29.0 mgl − 1) and high (>30 mgl − 1) TSM concentration for evaluating the performance of algorithms against different ranges of field measurements. The OCM-2 chlorophyll retrieval algorithm (OC4V4) showed a systematic and large overestimation of low chlorophyll values with r 2 = 0.607, root mean square error (RMSE) = 0.33 μgl − 1 and mean normalized bias (MNB) = 1.57 and consistent underestimation of high chlorophyll values with r 2 = 0.497, RMSE = 1.486 μgl − 1 and MNB = 0.52 especially at nearshore waters due to the interference of suspended matter and coloured dissolved organic matter. However, moderate range of chlorophyll values showed better performance of OC4V4 algorithm in chlorophyll retrieval with r 2 = 0.676, RMSE = 0.254 μgl − 1 and MNB = 0.09 when compared to low and high chlorophyll values. The TSM algorithm (modified algorithm of Tassan 1994) showed large underestimation in TSM retrievals and this was proved by the statistical results which shown maximum r 2 = 0.551 for low TSM values with less RMSE = 0.909 mgl − 1 and MNB = 0.616 error compared to moderate and high TSM values. OCM-2 retrieved TSM values were not well correlated with in-situ TSM concentration and constantly underestimates four times lesser than the in-situ measurements especially near the coast when TSM concentration was measured high. Though there was significant correlation exists between OCM-2 retrieved chlorophyll and TSM with in-situ measurements, the empirical algorithms employed did not give logical retrieval of both chlorophyll and TSM for the southwest Bay of Bengal (BoB). Thus, the present study revealed that the OCM-2 chlorophyll and TSM retrieval algorithms need to be tested further with extensive in-situ dataset around BoB to improve the regional algorithms for accurate measurements of chlorophyll and TSM in this region.

Shade tolerance of temperate Asian bamboos: a harbinger of their naturalization in Pacific Northwest coniferous forests?

Bamboos native to temperate East Asian coniferous forests arrive with increasing frequency in the United States as horticultural imports, and some are becoming naturalized locally. Given the strong floristic and physiognomic similarities between East Asian and western North American coniferous forests, we asked whether these introduced bamboos could tolerate the varied light regimes within coniferous forests in their new range. Seven temperate Asian bamboos and one North American bamboo (Arundinaria gigantea) were grown within shade structures in an experimental garden; these structures reduced ambient light to three light levels (50, 70, 90 % shade) that occur routinely within coniferous forests in the Pacific Northwest. Species’ responses under these light levels were measured by their light response curves to photosynthesis, resource allocation to light or carbon harvesting centers inferred by CO2 response curves, and shifts amongst forms of leaf Chlorophyll. Bashania fargesii has lower chlorophyll content and photosynthetic rates under high shade (90 %) relative to other Asian species and to B. fargesii grown in 50 and 70 % shade. Bashania fargesii, Sasa kurilensis and A. gigantea also displayed lower photosynthetic rates under 90 % shade compared to plants grown in 50 and 70 % shade and lower electron transport capacity under 70 and 90 % shade compared to plants grown in 50 % shade. In contrast, Pleioblastus chino, Pleioblastus distichus, Pseudosasa japonica, Sasa palmata and Sasaella ramosa display strong tolerance of low light. Our results indicate these five Asian bamboos (and others yet to be introduced) could skirt a major environmental barrier to new species establishment in these North American forests. Measuring a species’ light response curve offers a reliable, rapid means to assess an immigrant species’ potential to tolerate forests’ varied light regimes.

Bromus tectorum litter alters photosynthetic characteristics of biological soil crusts from a semiarid shrubland

Invasion by the exotic annual grass Bromus tectorum has increased the cover and connectivity of fine litter in the sagebrush steppes of western North America. This litter tends to cover biological soil crusts, which could affect their metabolism and growth. To investigate this possible phenomenon, biological soil crusts dominated by either the moss Bryum argenteum or the lichen Diploschistes muscorum were covered with B. tectorum litter (litter treatment) or left uncovered (control treatment) and exposed to natural field conditions. After periods of five and ten months, we removed the litter and compared the photosynthetic performance of biological soil crusts from the two treatments. Litter induced photosynthetic changes in our samples. In both B. argenteum and D. muscorum, biological soil crusts that had been covered with litter for ten months had lower rates of gross photosynthesis and lower chlorophyll content than control samples. Similarly in both biological soil crust types, litter reduced the rate of dark respiration. For D. muscorum, the reduction in dark respiration fully compensated for the decrease in gross photosynthesis, resulting in similar values of net photosynthesis in the two treatments. In contrast, for B. argenteum, net photosynthesis was four-times greater in the control than the litter treatment. Also under litter cover, D. muscorum showed three common adaptations to shade conditions: a decrease in the light compensation point, in the light intensity needed to achieve 95% of maximal net photosynthesis, and in the chlorophyll a/b ratio. None of these changes was apparent in B. argenteum. Overall, our results indicate that photosynthetic responses to the presence of litter varied among species of the crust biota and that the litter can reduce the photosynthetic capacity of biological soil crusts. These results help to explain field observations of decreases in biological soil crust cover and changes in biological soil crust composition with increases in litter cover, and suggest that the landscape-wide invasion by B. tectorum may have substantial effects on biological soil crust performance and therefore their capacity to function in semiarid shrublands.

Thermostability of chlorophylls in some native species of xerophytes

This study was carried out on eight wild species inhabited the tributaries of wadi Al Noman, at Holey Mecca in the western Kingdom of Saudi Arabia. The plant samples were collected at different locations, where laboratory analyses were included: the water content, chlorophyll content and its stability (CSI), , Mg ions, water soluble sugars and soluble proteins. The results showed that, the chlorophyll a content was higher than the chlorophyll b in the studied species. The maximum value of chlorophylls existed in C. colocyanthis and R. viscarius, whereas C. russeliana had low content of chlorophyll a and chlorophyll b. The chlorophyll a/b ratio was balanced by the chlorophyll stability to heat. The CSI of chlorophyll a was compensated by CSI of chlorophyll b and vice versa. The maximum values of total chlorophyll stability (a + b) was found in annuals C. colocynthis and D. innoxia, whereas C. russeliana had low CSI. The different chlorophyll parameters were mainly affected by the interaction between wadi and species, and the species factor played the subsidiary role on the chlorophyll content and chlorophyll a/b ratio in most floristic groups, except in case of chlorophyll a of dominant species the wadi factor was subsidiary. There was no significant effect of single factor on CSI of different groups. The correlation of Mg ions, soluble sugars and soluble proteins with total chlorophyll content and CSI were discussed.